Diffraction from Bilayers

Abstract

X‐ray diffraction provided a direct proof for the hypothesis that the basic structural element of biological membranes is
a bimolecular layer of phospholipid molecules. Diffraction from peptide–lipid mixtures can be used to study a great variety
of membrane problems.

Hydrophobic matching between lipids and peptides. (a) PtP of DMPC bilayers and DMPC bilayers containing gramicidin (gD) at 1:10 peptide/lipid molar ratio as a function of lamellar spacing D at specified temperatures (reproduced from Harroun et al., ). (b) PtP of pure lipid bilayers and bilayers containing WALP at 1:20 peptide/lipid molar ratio as a function of lamellar spacing D. The WALP density is the same as that of gramicidin channels, since the latter are dimers. The temperature of measurement
was 35°C for DMPC, and 30°C for DLPC and DTPC. (Reproduced from Weiss et al., .)

Figure 3.

Examples of membrane thickness measured as a function of the peptide concentration P/L. The hydrocarbon thickness h is PtP minus 1 nm (twice the phosphate to chain distance). Data of six different peptide/lipid systems are shown: alamethicin in
diphytanoyl phosphatidylcholine (DPhPC), alamethicin in a mixture of dioleoyl phosphatidylcholine (DOPC) and dioleoyl phosphatidylethanolamine (DOPE), melittin in DPhPC, melittin in DOPC, melittin in palmitoyl‐oleoyl phosphatidylcholine (POPC), and melittin in dieicosenoyl phosphatidylcholine (DiC20:1PC). The arrows indicate the threshold P/L* that were independently measured by detecting a change of peptide orientation upon the onset of pore formation (reproduced
from Huang et al., and Lee et al., ).

Figure 4.

Radial distribution functions of gramicidin obtained from the in‐plane scattering intensities of gramicidin embedded in DLPC and DMPC bilayers at specified temperatures. The position of the first peak gives the most probable nearest‐neighbour separation between
gramicidin channels in the bilayer. (Reproduced from Harroun et al., .)

Figure 5.

Neutron in‐plane scattering intensity of alamethicin pores in DLPC bilayer at P/L=1/10 hydrated with D2O (data +) or with H2O (data o). The broken line is a simulated structure factor of hard disks in two dimensions. The dotted line is the square
of the form factor for the pore. The solid line is the product of last two that fits the intensity curve. (Reproduced from
He et al., .)

Figure 6.

Structure of a fusion intermediate. (Left) Diffraction pattern from partially dehydrated multiple bilayers of diphytanoyl
phosphatidylcholine. (Right) The electron density distribution constructed from the diffraction pattern shows an interbilayer
structure called a stalk. (Reproduced from Yang and Huang, .)